1. Field of the Invention
This invention relates to integrated circuit (IC) packages technology, and more particularly, to a BGA (Ball Grid Array) integrated circuit package having a hear-dissipation device which can help enhance the thermal conductivity of the integrated circuit package and make the manufacture more cost-effective to implement.
2. Description of Related Art
A BGA integrated circuit package is a type of integrated circuit package that includes a plurality of electrically-conductive solder balls on the back side of a substrate for external connections of the integrated circuit chip mounted on the substrate. This BGA structure allows the integrated circuit package to be able to provide an increased number of I/O connections as compared to other types of integrated circuit packages while nevertheless having a large pitch. Moreover, since solder balls can be self-aligned to the bonding positions on the circuit board, the surface mounting of the BGA integrated circuit package on the circuit board is much easier to carry out than other types of integrated circuit packages, thus ensuring a high yield to the manufacture. Furthermore, during operation, the BGA integrated circuit package allows low inductance, low reactance, low eddy-current capacitance, and high heat-conductivity. All these benefits make the BGA integrated circuit package the mainstream of integrated circuit packaging technology. However, with a small package size, heat dissipation becomes a problem.
FIG. 1 is a schematic sectional diagram of a conventional BGA integrated circuit package with a heat-dissipation device. As shown, this BGA integrated circuit package 1 includes an encapsulant 2 (the encapsulated integrated circuit chip is not shown), a substrate 3, and an array of electrically-conductive balls 4. Further, the BGA integrated circuit package 1 includes a heat-dissipation device 10 which is encapsulated in the encapsulant 2 while having a surface exposed to the outside of the encapsulant 2 for heat dissipation to the atmosphere. The heat-dissipation device 10 is made of a heat-conductive material, such as copper (Cu).
One drawback to the forgoing heat-dissipation device 10, however, is that, since it is directly exposed to the atmosphere, the exposed surface would be easily oxidized, causing the heat-dissipation efficiency to be degraded. One solution to this problem is to coat nickel (Ni) on the exposed surface of the heat-dissipation device 10. In addition, for the purpose of strengthening the bonding between the unexposed surface of the heat-dissipation device 10 and the encapsulant 2, a black-oxidation process is performed on the unexposed surface of the heat-dissipation device 10. The involved process steps are depicted in the following with reference to FIGS. 2A-2E.
Referring first to FIG. 2A, in the first step, a copper-made base block 21 is prepared, whose bottom surface is coated with an insulative layer 22.
Referring next to FIG. 2B, in the subsequent step, a nickel-coating process is performed to coat a nickel layer 23 over the top surface of the base block 21.
Referring further to FIG. 2C, in the subsequent step, the entire insulative layer 22 is removed.
Referring next to FIG. 2D, in the subsequent step, a stamping process is performed to stamp the combined body of the base block 21 and the nickel layer 23 into a predefined shape, for example as the one illustrated.
Referring finally to FIG. 2E, in the last step, a black-oxidation process is performed on the bottom surface of the base block 21, whereby a black-oxidation layer 24 is formed on the bottom surface of the base block 21. This completes the fabrication of the heat-dissipation device 20.
Although the nickel layer 23 can help prevent the exposed surface of the heat-dissipation device 20 from oxidation, one drawback to the forgoing heat-dissipation device 20, however, is that the unexposed part of the nickel layer 23 encapsulated in the encapsulant has a poor bonding strength with the encapsulant, thus easily causing undesired delamination to the interface between the heat-dissipation device 20 and the encapsulant.
One solution to the foregoing problem is to perform a selective nickel-coating process, whose steps are depicted in the following with reference to FIGS. 3A-3F.
Referring first to FIG. 3A, in the first step, a copper-made base block 31 is prepared, whose upper and bottom surfaces are both coated with insulative layers 32.
Referring next to FIG. 3B, in the subsequent step, a de-coating process is performed to remove a selected part of the insulative layer 32 over the top surface of the base block 31.
Referring further to FIG. 3C, in the subsequent step, a nickel-coating process is performed to coat a nickel layer 33 over the removed part.
Referring further to FIG. 3D, in the subsequent step, all the remaining insulative layers 32 are removed with only the nickel layer 33 left.
Referring next to FIG. 3E, in the subsequent step, a stamping process is performed to stamp the base block 31 into a predefined shape, for example as the one illustrated.
Referring finally to FIG. 3F, in the last step, a black-oxidation process is performed on all the exposed surface of the base block 31 other than the part covered by the nickel layer 33, whereby a black-oxidation layer 34 is formed. This completes the fabrication of the heat-dissipation device 30.
By the foregoing method, the heat-dissipation device 30 has its exposed part coated with nickel layer 33 and all its unexposed part coated with black-oxidation layer 34, thereby allowing the heat-dissipation device 30 to be able to maintain good heat-dissipation efficiency all the time and also able to prevent the delamination from occurrence. One drawback to this method, however, is that, in the case that marking is required to be imprinted on the top side of the integrated circuit package, it would be difficult to do so since the marking ink would be easily erased from the nickel layer 33.
Still one drawback to the prior art is that it involves too many steps, which makes the manufacture process quite complex and thus cost-ineffective to implement.
It is therefore an objective of this invention to provide a BGA integrated circuit package with an improved heat-dissipation device whose exposed surface can be immune to oxidation.
It is another objective of this invention to provide a BGA integrated circuit package with an improved heat-dissipation device that can help prevent delamination from occurrence.
It is still another objective of this invention to provide a BGA integrated circuit package structure with an improved heat-dissipation device that can help prevent the marking ink imprinted thereon from erasure.
In accordance with the foregoing and other objectives, the invention proposes a new BGA integrated circuit package. The BGA integrated circuit package includes a substrate having a front side and a back side; an integrated circuit chip mounted on the front side of the substrate; a plurality of electrically-conductive contacts mounted on the back side of the substrate; a heat-dissipation device whose surface is coated with a palladium (Pd) layer and which is mounted on the front side of the substrate above the integrated circuit chip; and an encapsulant which encapsulates the integrated circuit chip and the heat-dissipation device therein. The heat-dissipation device can be manufactured in just two steps; a palladium-coating step and a stamping step, which allows the manufacture to be significantly reduced in complexity than the prior art.